DAB radio, a Technial review (warning long)

[pablohoney]

Hi all (firstly sorry for the length of this post! )

Im writing this because i recently replaced my Head Unit and decided to go for a DAB radio. I have been really disappointed in the DAB sound and thought I'd share my findings. DAB is getting a huge amount of marketing in the UK at present and imho a lot of it is misleading. The key sells are "Digital Sound Quality" which most people would assume to be CD like, and "Crystal Clear Reception"

First it'll helps to explain how DAB actually works, unlike FM where each individual station occupies it's own frequency on the spectrum, DAB broadcasts in several multiplexed feeds, these are called "Ensembles". Each Ensemble is a digital stream that contains several stations, your radio extracts only the part of the stream it needs for the station you want to hear and ignores the rest. The Ensemble is a fixed size (bitrate) of data, therefore broadcasters had to make a decision regarding how many stations to squeeze into each Ensemble, of course what they did was to maximize the number of stations, rather than having a reduced number at a higher bitrate and therefore sound quality (after all more stations=more revenue).

"Sound Quality".

When DAB was introduced the recommended bitrate was 160kbps per station, however a few years on they are all down at 128kbps per station (even lower for the talk radio style and special interest stations). Even the BBC has had to drop its high-quality Radio3 from 190kbps to 160kbps and this drops further to 128kbps when they "borrow" some bandwidth when Radio 5 Live Extra is broadcasting.

Anyone into MP3 (iPods etc...) will be aware that 128kbps is considered as-low-as-you-want-to-go for music, and lots of people prefer to encode to a higher bitrate. The situation would probably be acceptable if DAB was delivering 128kbps MP3, however DAB broadcasts using the less efficient MP2 compression, this Is accepted as being around 25% less efficient than MP3, so to put DAB into perspective you should probably think of something around a 96kbps MP3.

At this low bitrate you'll certainly notice Sibilance in the treble leading to a slight lispy effect on DJ's voices, and if like me you're into Guitar based groups then you'll sometimes have trouble picking out instruments and even vocals from what becomes a frustratingly muddled sound.

"Crystal Clear Reception".

It is certainly true that you won't hear any Hiss on a DAB broadcast, but you almost certainly will experience drop-out, and the weird effects we've all heard on our mobile phones from time to time, I guess this should be called digital-noise.


Pros of DAB

Increased number of stations
Increased footprint of some stations

Cons of DAB

Sound quality not what it should be. (a strong FM station will sound better)
Certainly not without interference.
Will the situation get even worse as they add more stations?

So why did I get a DAB radio?, Radio 5 - even a 60kbps DAB feed sounds better than MW, and the London FM station XFM is a lousy FM signal in my area.

I'm not saying don't get a DAB radio, but don't go assuming it'll amaze you!

Paul.

[0007]

Pablohoney - thanks for a very lucid and useful assessment.

[monsta]

I must admit I have often wondered how good DAB would be in a car!

I have used a Wavefinder on a PC to pick up DAB and found the reception to be OK, but interference to be far more annoying than it's equivalent on FM.

Good post, thanks for the info

[SteveM3]

Very good explanation. I thought I was a lone voice in the wilderness about a lot of
market crap about digital transmissions, TV and radio. Digital is NOT better, it is an
improvement if you live in an area with a poor signal. At the moment if you live in a
good signal area stick to analogue. Where digital scores is technology is always
coming down in price and one day the bitrate will be so high as to banish analogue
the way of monochrome TV. Not yet though.

[pablohoney]

Steve,

Don't worry you're not alone!

What bothers me is that with any new broadcast system you only get one chance to define the standard and then once people buy the receivers you're obliged to stick with it for decades.

In the case of DAB it's barely a few years old, has just started to penetrated the market and it's already outdated, the bandwidth available for stations can't just be increased from nowhere and the compression they used is ancient, if they'd based it around MP3 or AAC then it would have made more use of the limited resources.

I guess it comes down to sticking the word Digital on something and hoping no-one questions that there are rather a lot of factors that dictate the quality of a Digital sound. I'm really surprised to see the mighty BBC throwing away their engineering principles though! if they'd left out one or two new stations on their DAB ensemble they could have offered the quality we've all been promised and they'd have really stood out above the commercial stations.

[Mini-Medic]

Thanks for a very useful post. I have been considering getting rid of my boost h/u and swapping it for a DAB unit (probably the Woodstock), on the assumption that the clarity of sound would be better than an FM unit. Other that the extra stations that I'll be able to pick up, sounds like I'm better off sticking with FM.

Might get a decent unit with MP3 and stick to my "homemade" radio station

Pablo - which head unit do you have? And what type of DAB ariel are you using?

[Hat]

good info but i'd be interested to know where it comes from. plus are you speaking just from experience of the set up in your car or from a broader perspective?

[ButtonIt]

To be honest I've not had any quality issues with my DAB radio. I find no matter where I go for example Radio1 sounds much better on DAB than FM??

[joebickley]

Good Post Pablo, Which DAB aerial do you have? (sure i asked this before but i forgot )